Early Steps in Specific Tumor Cell Lysis by Sensitized Mouse T Lymphocytes

Abstract

Abstract It has previously been shown by several investigators that Mg++ in the absence of appreciable Ca++ is sufficient to support the formation of specific adhesions between cytolytic T lymphocytes (CTL) and tumor target cells but that programming of the targets for lysis is strongly Ca++ dependent. However, we recently found that Ca++, in the presence of suboptimal concentrations of Mg++, is capable of synergizing with Mg++ in supporting adhesion formation. The latter observation raised the possibility that the structure of the adhesion in the absence of Ca++ might be unphysiologic and incompatible with programming for lysis. Thus it was conceivable that the role of Ca++ in programming for lysis might be limited to its demonstrated role in adhesion. In the present report we have examined the abilities of other alkaline earth metals to substitute for calcium in supporting adhesion formation and programming for lysis. In the presence of Mg++ at a concentration optimal to support adhesion, Sr++ could replace Ca++ in programming for lysis. The concentration of Sr++ required for maximum cytolysis was 5- to 20-fold greater than the optimum Ca++ concentration; nevertheless when Sr++ was present at an optimum concentration, the amount of lysis was identical to that observed in the presence of an optimum concentration of Ca++. In contrast to its ability to replace Ca++ in programming for lysis, Sr++ could not substitute for Ca++ in potentiating adhesion formation in the presence of suboptimal Mg++. Ba++ could not substitute for Ca++ in either adhesion formation or programming for lysis but inhibited both in the presence of Ca++. Likewise, high concentrations of Mg++ in the absence of Ca++ did not enhance programming for lysis. The ability of Sr++ to replace Ca++ in cytolysis but not in adhesion formation indicates that the role of Ca++ in programming for lysis is distinct from its demonstrated role in adhesion and the calcium is required only at the former site. It is possible that the role of Ca++ in programming for lysis is to act as a co-factor essential to the activity of a CTL surface protein involved in the lytic mechanism. Alternatively, Ca++ influxes into CTL may trigger activation of the lytic mechanism in a manner analogous to the stimulus-secretion coupling seen in many secretory phenomena. The observation that the order of efficacy of alkaline earth metals is supporting programming for lysis is Ca++ τ Sr++ τ Ba++ or Mg++ is compatible with either possibility.